There are a variety of different applications for a light shield to limit the light impinging upon or radiating from a light interface such as a lamp, a camera lens, or the viewing screen of an oscilloscope or television display. In some of these applications, adjustability of the shield is a prime requirement, to meet varying operating conditions. Thus, a broad pattern of light from a lamp may be desirable in one instance, but a much narrower pattern from the same lamp may be required in another instance. On a camera, the light shield may function best in a contracted configuration for a narrow angle lens, whereas a wide angle lens may require that the light shield be opened up substantially. For a television receiver, a relatively open configuration may provide the best viewing when ambient light is minimal and several people are observing the television screen, whereas under harsh lighting conditions with a single viewer it may be preferable to narrow the shield down substantially.
Similar situations apply for shields or deflectors in other applications. Thus, an air outlet or inlet in one system may have to fit a narrow, confined pattern; in another application, a broad, spreading deflector may be needed. Sound systems may also demand a variety of interface shield or deflector configurations.
Several effective light shields for television receivers, utilizing three hinged shield panels connected at the corners by angular corner units are described in Rose U.S. Pat. No. 3,062,917. Those light shields are quite effective for many television uses, but lack of versatility necessary for other applications, especially if expansion-contraction range requirements are substantial and the dimensions of the shield are relatively large in relation to the dimensions of the interface with which it is employed. In particular, the light shields disclosed in the patent do not provide adequate means for maintaining the shield panels and corner units in accurate alignment throughout a large range of shield panel movements.
Another problem encountered in many shield and deflector applications is the need to hold the shield panels in position over a wide range of adjustment. A related difficulty is the tendency of an adjustable shield to open or close spontaneously due to vibration, movement of the interface apparatus with which the shield is associated, and other external factors; ideally, the shield, when moved to a new angular alignment, should remain steady in that alignment even though it may be moved about or subjected to vibration, jarring, or other disturbance.
In a shield of substantial depth, relative to the size of the interface with which it is employed, problems of interference between the elements used to close the corners of the shield are frequently encountered. Another difficulty arises from the fact that with any substantial change of the angular alignment of the side panels, the angles of the smaller panels used in the corner units changes substantially.